In charged particle radiation devices such as scanning electron microscopes, ion microscopes, semiconductor test devices, a sample is irradiated with a charged particle radiation beam generated under an ultrahigh vacuum environment inside a charged particle optical lens barrel and secondary electrons emitted or reflected electrons backscattered from the sample are detected to obtain an observed image of the sample. Therefore, if the charged particle optical lens barrel vibrates relative to the sample, the position irradiated with the charged particle radiation beam frequently changes, resulting in the observed image being deformed and/or an edge of a pattern looking vibrating, and if plural observed images are added up, the image resulting from the addition including a blurred edge. As described above, vibration of a charged particle optical lens barrel causes deterioration in image quality of observed images, and furthermore, may become one of the causes of a decrease in resolution of the charged particle radiation device, and thus, it is necessary to make an effort to damp such vibration.
Effects imposed by vibration of a charged particle optical lens barrel on a charged particle radiation device will be described taking a semiconductor test device as an example. Semiconductor test devices are devices that observe defects in patterns in semiconductor devices formed by exposure on a wafer, and classify the defects depending to their types. In recent years, accompanied by miniaturization of semiconductor devices, it is necessary that the sizes of defects to be detected be also reduced. At the same time, it is necessary that the number of defects detected per unit time be increased. Furthermore, it is expected that the most common size of wafers for semiconductor devices will transition from φ300 mm to φ450 mm. As described above, it is necessary to achieve a high resolution and a high throughput while the sizes of the devices are increased.
In a semiconductor test device, it is necessary to move a stage with a wafer mounted thereon to an observation position. Here, if a sample chamber is vibrated by a reaction force generated when the stage is halted, resulting in the charged particle optical lens barrel vibrating, the quality of images in the test device is lowered as described above. For further throughput enhancement, it is necessary to promptly damp the natural vibration of the charged particle optical lens barrel immediately after the stage is moved to a certain observation position and halted there.
Patent Literatures 1 to 3 disclose techniques for damping of vibration of charged particle optical lens barrels as described below.
Patent Literature 1 discloses an electron beam lithographic device that provides a vibration damping effect enhanced by provision of a vibration damping material layer on an upper surface of a vacuum chamber or a charged particle optical lens barrel.
Patent Literature 2 discloses an electron beam lithographic device in which an upper portion of a charged particle optical lens barrel and four corners of a sample chamber are connected via stays to provide an enhanced vibration damping effect.
Patent Literature 3 discloses a charged particle radiation device in which an ion pump secured to a charged particle optical lens barrel is supported using a frame (support member for the ion pump) secured on a sample chamber, and a damper using a viscoelastic material is inserted between a case and a yoke of the ion pump to suppress external vibration received by the frame or transmission of vibration from the sample chamber to the charged particle optical lens barrel.